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Abstract:

The present invention relates to a cell selection method of a terminal in
a heterogeneous network, and cell selection method of a terminal in a
heterogeneous network according to the present invention includes
receiving a measurement restriction pattern from a base station; and
selecting a cell based on the measurement restriction pattern. According
to an embodiment of the present invention, it is possible to select a
cell accurately and efficiently.

Claims:

1. A cell selection method of a terminal in a heterogeneous network, the
method comprising: receiving a measurement restriction pattern from a
base station; and selecting a cell based on the measurement restriction
pattern.

2. The method of claim 1, wherein selecting comprises: checking
measurement-restricted subframes based on the measurement restriction
pattern; measuring cell signal at measurement-restricted subframes; and
selecting the cell based on the measured cell signal.

3. The method of claim 1, wherein selecting comprises: discriminating
between measurement restricted and measurement non-restricted subframes
based on the measurement restriction pattern; measuring cell signal at
the restricted and non-restricted subframes; and selecting, when a
difference between cell signals measured at the restricted and
non-restricted subframes is greater than a threshold value, the cell
based on the cell signal measured at the restricted subframe.

4. The method of claim 3, wherein selecting comprises selecting, when a
difference between cell signals measured at the restricted and
non-restricted subframes is equal to or less than a threshold value, the
cell based on the cell signal measured at the non-restricted subframe.

5. The method of claim 1, wherein selecting comprises: discriminating
between measurement restricted and measurement non-restricted subframes
based on the measurement restriction pattern; measuring cell signal at
the non-restricted subframe; and selecting, when the measured cell signal
is equal to or greater than a predetermined threshold value, the cell
based on the cell signal measured at the non-restricted subframe.

6. The method of claim 5, wherein selecting comprises selecting, when the
measured cell signal is less than the threshold value, the cell based on
the cell signal measured at the restricted subframe.

7. The method of claim 3, further comprising receiving the predetermined
threshold value.

8. The method of claim 5, further comprising receiving the predetermined
threshold value.

9. A terminal for selecting a cell in a heterogeneous network, the
terminal comprising: a transceiver which receives a measurement
restriction pattern from a base station; and a controller which selects a
cell based on the measurement restriction pattern.

10. The terminal of claim 9, wherein the controller checks
measurement-restricted subframes based on the measurement restriction
pattern, measures cell signal at measurement-restricted subframes, and
selects the cell based on the measured cell signal.

11. The terminal of claim 9, wherein the controller discriminates between
measurement restricted and measurement non-restricted subframes based on
the measurement restriction pattern, measures cell signal at the
restricted and non-restricted subframes, and selects, when a difference
between cell signals measured at the restricted and non-restricted
subframes is greater than a threshold value, the cell based on the cell
signal measured at the restricted subframe.

12. The terminal of claim 11, wherein the controller selects, when a
difference between cell signals measured at the restricted and
non-restricted subframes is equal to or less than a threshold value, the
cell based on the cell signal measured at the non-restricted subframe.

13. The terminal of claim 9, wherein the controller discriminates between
measurement restricted and measurement non-restricted subframes based on
the measurement restriction pattern, measures cell signal at the
non-restricted subframe, and selects, when the measured cell signal is
equal to or greater than a predetermined threshold value, the cell based
on the cell signal measured at the non-restricted subframe.

14. The terminal of claim 13, wherein the controller selects, when the
measured cell signal is less than the threshold value, the cell based on
the cell signal measured at the restricted subframe.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a wireless communication system
and, in particular, to a cell selection method and apparatus of a
terminal in a Long Term Evolution (LTE) system of heterogeneous network.

[0003] 2. Description of the Related Art

[0004] Recently, wireless communication technology has advanced rapidly.
With this rapid advance, the communication systems have evolved. Among
the recent wireless communication technologies, Long Term Evolution (LTE)
is a promising 4th Generation mobile communication standard. An LTE
system may include various types of base stations such as macro base
station, pico base station, and femto base station according to their
deployment positions or purposes. A network in which the diverse types of
base stations coexist is referred to as Heterogeneous Network (HetNet).
The diameter pico/femto cell is small as compared to that of the macro
cell.

[0005] In the heterogeneous network, the coverage of the pico/femto base
station may be overlapped with or included in the coverage of the macro
cell. In this case, it is difficult to expect accurate signal measurement
due to the inter-cell interference. In order to solve this problem,
inter-cell interference coordination, i.e. Enhanced Inter Cell
Interference Coordination (eICIC), technology is used.

[0006] Almost Blank Subframe (ABS) is one of the key techniques in the
eICIC technology. In LTE, transmission is performed in unit of subframe.
ABS is a technique for muting transmission in the serving cell or
neighboring cell at a specific subframe. ABS aims to make it possible for
the terminal to measure received signal without interference at the
corresponding subframe.

[0007] FIG. 1 is a diagram illustrating the HetNet to which ABS technique
of eICIC technology is applied.

[0008] Referring to FIG. 1, a femto Closed Subscriber Group (CSG) base
station 103 allowing access to restricted users is located within the
coverage of the macro base station 101. In the case that the non-CSG
terminal 105 in communication with the macro base station 101 moves to
approach the femto CSG base station 103, the non-CSG terminal 105 may
undergo a problem in communication due to the interference from the femto
CSG base station 103. In this case, the macro base station 101 notifies
the terminal 105 of a measurement-restricted subframe pattern 107 in the
form of a bitmap. If the pattern is received, the terminal 105 suspends
measurement at the subframes indicated by 0 in the pattern 107 and
performs measurement only at the subframes indicated by 1. The femto CSG
base station 130 incurring interference does not transmit signal almost
at the subframe indicated by 1 (ABS) so as to avoid interference. The
terminal 105 is capable of measuring signal in the interference-mitigated
environment.

[0009] The eICIC technologies in HetNet that are known so far are almost
related to the terminal (UE) connected to the network. According to the
conventional method, the base station can control the UE connected to the
network directly so as to mitigate interference by controlling the UE.
However, there is a need of applying the eICIC of HetNet to the UEs in
idle mode that are not controlled by the network. In the HetNet system,
the Reference Signal Received Quality/Reference Signal Received Power
(RSRQ/RSRP) of the UEs in idle mode varies at every subframe, this
influence the cell selection or reselection result. There is therefore a
need of determining the subframe for performing cell reselection or
reselection based on the signal strength measured thereat. Accordingly,
there is a need of modification in UE operation.

DISCLOSURE OF INVENTION

[0010] Technical Problem

[0011] The present invention has been made in an effort to solve the above
problem, and it is an object of the present invention to provide a cell
selection method and apparatus of a UE for selecting a cell efficiently
and accurately in case of using eICIC technology in the wireless mobile
communication system of HetNet environment.

[0012] Solution to Problem

[0013] In order to accomplish the above object, a cell selection method of
a terminal in a heterogeneous network includes receiving a measurement
restriction pattern from a base station; and selecting a cell based on
the measurement restriction pattern.

[0014] In order to accomplish the above object, a terminal for selecting a
cell in a heterogeneous network includes a transceiver which receives a
measurement restriction pattern from a base station; and a controller
which selects a cell based on the measurement restriction pattern.

[0015] Advantageous effects

[0016] According to an embodiment of the present invention, the terminal
is capable of selecting a cell efficiently and accurately in a
heterogeneous network environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a diagram illustrating the HetNet to which ABS technique
of eICIC technology is applied.

[0018] FIG. 2 is a signaling diagram illustrating the measurement
procedure of the cell (re)selection method according to the first
embodiment of the present invention.

[0019] FIG. 3 is a signaling diagram illustrating the measurement
procedure of the cell (re)selection method according to the second
embodiment of the present invention.

[0020] FIG. 4 is a flowchart illustrating the measurement procedure of the
cell (re)selection method according to the third embodiment of the
present invention.

[0021] FIG. 5 is a flowchart illustrating the measurement procedure of the
UE according to the first embodiment of the present invention.

[0022] FIG. 6 is a flowchart illustrating the measurement procedure of the
UE according to the second embodiment of the present invention.

[0023] FIG. 7 is a flowchart illustrating the measurement procedure of the
UE according to the third embodiment of the present invention.

[0024] FIG. 8 is a block diagram illustrating the configuration of the UE
according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0025] Exemplary embodiments of the present invention are described with
reference to the accompanying drawings in detail.

[0026] Detailed description of well-known functions and structures
incorporated herein may be omitted to avoid obscuring the subject matter
of the present invention. This aims to omit unnecessary description so as
to make the subject matter of the present invention clear.

[0027] For the same reason, some of elements are exaggerated, omitted or
simplified in the drawings and the elements may have sizes and/or shapes
different from those shown in drawings, in practice. The same reference
numbers are used throughout the drawings to refer to the same or like
parts.

[0028] Descriptions are made of the cell selection method and apparatus
according to the embodiments of the present invention hereinafter with
reference to accompanying drawings.

[0029] Detailed description of well-known functions and structures
incorporated herein may be omitted to avoid obscuring the subject matter
of the present invention. Exemplary embodiments of the present invention
are described hereinafter with reference to the accompanying drawings in
detail.

[0030] FIG. 2 is a signaling diagram illustrating the measurement
procedure of the cell (re)selection method according to the first
embodiment of the present invention.

[0031] The UE 201 receives information on a measurement restriction
pattern, i.e. the pattern related to the measurement restriction, from a
base station (eNB) 203 at step 205. The measurement restriction pattern
is the pattern indicating subframes at which the UE performs/suspends
measurement. The UE 201 is capable of receiving the measurement
restriction pattern through unicast, broadcast, or combination thereof.
In both the connected mode and idle mode, the UE 201 is capable of
receiving the measurement restriction pattern through broadcast from the
eNB 203. In the connected mode, the UE 201 is capable of receiving the
measurement restriction pattern through unicast.

[0032] In order to transmit the measurement restriction pattern, i.e. the
pattern related to the measurement restriction, at least one of following
signaling schemes can be used.

[0033] In order to transmit the measurement restriction pattern, Radio
Resource Management/Radio Link Management (RRM/RLM) resource restriction
of the serving cell can be used. The RRM/RLM resource restriction is a
bitmap having a size of 40 bits. Each bit of the bitmap corresponds to a
subframe. In order to manage mobility, when measuring the serving cell
signal strength, the UE 201 performs measurement only at the subframes
indicated by 1 in the bitmap.

[0034] In order to transmit the measurement restriction pattern, the
RRM/RLM resource restriction of a neighbor cell. The RRM/RLM resource
restriction of the neighbor cell is a bitmap having the size of 40 bits.
Each bit of the bitmap corresponds to a subframe. In order to manage
mobility, when measuring the serving cell signal strength, the UE 201
performs measurement only at the subframes indicated by 1 in the bitmap.

[0035] In order to transmit the measurement restriction pattern, Channel
Quality Information/Channel State Information (CQI/CSI) resource
restriction can be used. The CQI/CSI resource restriction of the serving
cell is a bitmap having the size of 40 bits. Each bit of the bitmap
corresponds to a subframe. When measuring CQI/CSI for the serving cell,
the UE 201 performs measurement only at the subframes indicated by 1 in
the bitmap.

[0036] If the information on the measurement restriction pattern is
received as described above, the UE 201 checks the subframes at which
measurement is restricted in the time domain at step 207. The UE 201
performs measurement only at the restricted subframes and uses the
measurement result for cell selection or reselection at step 209.

[0037] FIG. 3 is a signaling diagram illustrating the measurement
procedure of the cell (re)selection method according to the second
embodiment of the present invention.

[0038] The UE 301 receives the information on the pattern related to
measurement, i.e. measurement restriction pattern, from the eNB 303 at
step 305. The UE 301 is capable of receiving the measurement restriction
pattern through unicast, broadcast, or combination thereof. In both the
connected mode and idle mode, the UE 301 is capable of receiving the
measurement restriction pattern from the eNB 303 through broadcast. In
the connected mode, the UE 301 is capable of receiving the measurement
restriction pattern through unicast. If the information on the
measurement restriction pattern is received, the UE 301 checks the
subframes at which measurement is restricted at step 307. The UE 301
performs measurement at both the restricted subframes and the
non-restricted subframes and uses the measurement result acquired at the
non-restricted subframes for cell selection or reselection at step 309.

[0039] The UE 301 compares the RSRQs (or RSRPs) measured at the restricted
and non-restricted subframes with each other to determine whether the
difference therebetween is greater than a threshold value A at step 311.
Here, the threshold value A can be signaled through a separate message.
According to a modified embodiment, the UE 301 is capable of utilizing a
predetermined threshold value A. In the case that the threshold value is
signaled through a separate message, the UE 301 is capable of receiving
the threshold value form the eNB 303 through unicast, broadcast, or
combination thereof. In both the connected mode and idle mode, the UE 301
is capable of receiving the threshold value A through broadcast from the
eNB 303. In the case that the difference between measurement results is
greater than the threshold value A (or equal to the threshold value), the
UE 301 uses the measurement result acquired at the restricted subframe
for cell selection or cell reselection at step 313.

[0040] FIG. 4 is a flowchart illustrating the measurement procedure of the
cell (re)selection method according to the third embodiment of the
present invention.

[0041] The UE 401 receives the measurement restriction pattern from the
eNB 403 at step 405. The UE 401 is capable of receiving the measurement
restriction pattern through unicast, broadcast, or combination thereof.
In both the connected mode and idle mode, the UE 401 is capable of
receiving the measurement restriction pattern through broadcast from the
eNB 403. In the connected mode, the UE 401 is capable of receiving the
measurement restriction pattern from the eNB 403 through unicast. If the
information on the measurement restriction pattern is received, the UE
401 checks the subframes at which measurement is restricted at step 407.
The UE 301 performs measurement at the non-restricted subframes and uses
the measurement result for cell selection or reselection at step 409.

[0042] If the signal strength (e.g. RSRQ) measured at the non-restricted
subframe is less than a threshold value B (or equal to the threshold
value B), the UE 401 performs measurement at the restricted subframe to
use the measurement result for cell selection or cell reselection. Here,
the threshold value B can be signaled through a separate message.
According to a modified embodiment, the UE 401 is capable of using a
predetermined value as the threshold value B. In the case that the
threshold value B is signaled through a separate message, the UE 401 in
the connected mode or the idle mode is capable of receiving the threshold
value B through broadcast from the eNB 403. In the connected mode, the UE
401 is capable of receiving the threshold value B through unicast from
the eNB 403.

[0043] FIG. 5 is a flowchart illustrating the measurement procedure of the
UE according to the first embodiment of the present invention.

[0044] The operation of the UE 201 starts at step 501. The UE 201 receives
the information on the pattern related to measurement at step 503. Next,
the UE 201 performs measurement only at the measurement-restricted
subframes indicated in the pattern and uses the measurement result for
cell selection or reselection at step 505.

[0045] FIG. 6 is a flowchart illustrating the measurement procedure of the
UE according to the second embodiment of the present invention.

[0046] The operation of the UE 301 starts at step 601. The UE 301 receives
the measurement restriction pattern at step 603. The UE 301 performs
measurement at both the restricted subframes and non-restricted subframes
indicated by the measurement restriction pattern at step 605. After
measurement, the UE 301 calculates the difference between the measurement
results (RSRPs or RSRQs) at the restricted and non-restricted subframes
at step 607. The UE 301 determines whether the measurement result
difference is greater than the threshold value A (or equal to the
threshold value A) at step 609. If the measurement result difference is
greater than the threshold value A, the UE 301 uses the measurement
result acquired at the restricted subframe for cell selection or
reselection at step 613. Otherwise, if the measurement result difference
is less than the threshold value A, the UE 301 uses the measurement
result acquired at the non-restricted subframe for cell selection or
reselection.

[0047] FIG. 7 is a flowchart illustrating the measurement procedure of the
UE according to the third embodiment of the present invention.

[0048] The operation of the UE 401 starts at step 701. The UE 401 receives
the measurement restriction pattern at step 703. The UE 401 performs
measurement at the non-restricted subframe indicated by measurement
restriction pattern and uses the measurement result for cell selection or
reselection at step 705. The UE 401 determines whether the RSRQ value of
the measurement result is less than the threshold value B (or equal to
the threshold value B) at step 707. If the RSRQ value is greater than the
threshold value B, the UE 401 returns the procedure to step 705 to
perform measurement at the non-restricted subframes continuously and use
the measurement result for cell selection or reselection. If the RSRQ
value is less than the threshold value B, the UE 401 performs measurement
at the restricted subframe and uses the measurement result for cell
selection or reselection at step 709.

[0049] FIG. 8 is a block diagram illustrating the configuration of the UE
according to an embodiment of the present invention.

[0050] The higher layer device 805 transmits and receives data through
higher layer. The control message processor 807 transmits and receives
data through control messages. The control unit 809 controls the
multiplexer/demultiplexer 803 to multiplex the data and transmit the data
through the transceiver 801. The control unit 809 controls the
transceiver 801 to receive a physical signal and controls the
multiplexer/demultiplexer 803 to demultiplex the received signal. The
control unit 809 transfers the messages to the higher layer device 805 or
control message processor 807 according to the information on the
messages.

[0051] According to an embodiment of the present invention, if the
information message about the measurement restriction pattern from the
eNB, the control message processor 807 of the UE analyzes the message to
differentiate between the restricted subframes and non-restricted
subframes. The control message processor 807 notifies the controller 809
of the type of subframe at which measurement is to be performed.

[0052] According to the first embodiment, the control message processor
807 instructs the controller 809 to perform measurement only at the
restricted subframes for cell selection and reselection. According to the
second embodiment, the control message processor 807 instructs the
controller 809 to perform measurement at both the restricted and
non-restricted subframes. The control message processor 807 receives the
measurement result from the controller 809 back and instructs the
controller 809 to perform measurement at the restricted subframe or not
based on the measurement result difference. According to the third
embodiment, the control message processor 807 receives the measurement
result from the controller 809 and instructs the controller 809 to
perform measurement at the restricted subframes when the RSRQ is less
than the threshold value B.

[0053] With the proposed method, the UE in the idle mode is capable of
measuring signal according to the measurement restriction pattern of
eICIC and performing cell (re)selection in consideration of the
interference from the neighbor cells in the HetNet environment, resulting
in improvement of cell selection efficiency and accuracy.

[0054] Advantages and features of the present invention and methods of
accomplishing the same may be understood more readily by reference to the
following detailed description of exemplary embodiments and the
accompanying drawings. The present invention may, however, be embodied in
many different forms and should not be construed as being limited to the
exemplary embodiments set forth herein. Rather, these exemplary
embodiments are provided so that this disclosure will be thorough and
complete and will fully convey the concept of the invention to those
skilled in the art, and the present invention will only be defined by the
appended claims. Like reference numerals refer to like elements
throughout the specification.

[0055] The present invention is described with reference to accompanying
drawings illustrating [tile of the invention] in the embodiment of the
present invention.

[0056] It will be understood that each block of the flowchart
illustrations and/or block diagrams, and combinations of blocks in the
flowchart illustrations and/or block diagrams, can be implemented by
computer program instructions. These computer program instructions may be
provided to a processor of a general purpose computer, special purpose
computer, or other programmable data processing apparatus to produce a
machine, such that the instructions, which execute via the processor of
the computer or other programmable data processing apparatus, create
means for implementing the functions/acts specified in the flowchart
and/or block diagram block or blocks. These computer program instructions
may also be stored in a computer-readable memory that can direct a
computer or other programmable data processing apparatus to function in a
particular manner, such that the instructions stored in the
computer-readable memory produce an article of manufacture including
instruction means which implement the function/act specified in the
flowchart and/or block diagram block or blocks. The computer program
instructions may also be loaded onto a computer or other programmable
data processing apparatus to cause a series of operational steps to be
performed on the computer or other programmable apparatus to produce a
computer implemented process such that the instructions which execute on
the computer or other programmable apparatus provide steps for
implementing the functions/acts specified in the flowchart and/or block
diagram block or blocks.

[0057] Furthermore, the respective block diagrams may illustrate parts of
modules, segments or codes including at least one or more executable
instructions for performing specific logic function(s). Moreover, it
should be noted that the functions of the blocks may be performed in
different order in several modifications. For example, two successive
blocks may be performed substantially at the same time, or may be
performed in reverse order according to their functions.

[0058] The term "module" according to the embodiments of the invention,
means, but is not limited to, a software or hardware component, such as a
Field Programmable Gate Array (FPGA) or Application Specific Integrated
Circuit (ASIC), which performs certain tasks. A module may advantageously
be configured to reside on the addressable storage medium and configured
to be executed on one or more processors. Thus, a module may include, by
way of example, components, such as software components, object-oriented
software components, class components and task components, processes,
functions, attributes, procedures, subroutines, segments of program code,
drivers, firmware, microcode, circuitry, data, databases, data
structures, tables, arrays, and variables. The functionality provided for
in the components and modules may be combined into fewer components and
modules or further separated into additional components and modules. In
addition, the components and modules may be implemented such that they
execute one or more CPUs in a device or a secure multimedia card.

[0059] The foregoing disclosure has been set forth merely to illustrate
the invention and is not intended to be limiting. Since modifications of
the disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention should
be construed to include everything within the scope of the appended
claims and equivalents thereof.

[0060] Although exemplary embodiments of the present invention have been
described in detail hereinabove with specific terminology, this is for
the purpose of describing particular embodiments only and not intended to
be limiting of the invention. While particular embodiments of the present
invention have been illustrated and described, it would be obvious to
those skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the invention.

[0061] Although the description has been made with reference to particular
embodiments, the present invention can be implemented with various
modification without departing from the scope of the present invention.
Thus, the present invention is not limited to the particular embodiments
disclosed but will include the following claims and their equivalents.